1. Field of the Invention
The present invention relates to a motor drive circuit.
2. Description of the Related Art
There are cases where a motor is locked and is not driven to rotate even though a drive circuit is supplying a drive current to a drive coil. In this case, an overcurrent might flow through the drive coil thereby burning out the drive coil, or an overcurrent might flow through the drive circuit thereby causing the drive circuit to generate heat and break down.
As a protection circuit configured to stop supply of a drive current to the drive coil performed by the drive circuit if a motor is locked, (hereinafter referred to as a protective operation), known is a locking protection circuit as described in Japanese Patent Laid-Open Publication No. 2000-188893, for example.
The locking protection circuit used to stop supply of the drive current to the drive coil performed by the drive circuit if a rotation signal indicating rotation of the motor is not generated for a certain time period, although the drive current is being supplied to the drive coil.
For the purpose of suppressing vibration, noise or the like at the start of the motor, for example, the motor may be started slowly in some cases, setting a time period, from a time when power is turned on till a time when a power supply voltage reaches a steady voltage, at approximately several seconds.
In such a power supply, however, if the locking protection circuit described in Japanese Patent Laid-Open Publication No. 2000-188893 is employed, such a low power supply voltage period during which a drive current required for normal motor rotation cannot be generated results in a long period, in the time period from the time when power is turned on till the time when the power supply voltage reaches the steady voltage, so that a rotation signal indicating motor rotation is not generated in that time period, thereby causing a possibility of misjudgment that the motor is locked although the motor is not locked in actuality.